Photoactive adhesion promoter in a slam

ABSTRACT

A semiconductor process technique to help reduce semiconductor process effects, such as undesired line edge roughness, insufficient lithographical resolution, and limited depth of focus problems associated with the removal of a photoresist layer. More particularly, embodiments of the invention use a photoacid generator (PAG) material in conjunction with a sacrificial light absorbing material (SLAM) to help reduce these and other undesired effects associated with the removal of photoresist in a semiconductor manufacturing process. Furthermore, embodiments of the invention allow a PAG to be applied in a semiconductor manufacturing process in an efficient manner, requiring fewer processing operations than typical prior art techniques.

FIELD

Embodiments of the invention relate to the field of semiconductormanufacturing. More particularly, embodiments of the invention relate toa photoactive adhesion promoter to facilitate solubility of photoresiston a semiconductor wafer.

BACKGROUND

As feature sizes continue to decline in modern photolithographicsemiconductor manufacturing processes, effects, such as undesired lineedge roughness, insufficient lithographical resolution, and limiteddepth of focus problems can increase. More particularly, photoresistimage footprints may become increasingly difficult to control assemiconductor device features become smaller and closer together.

Adhesion promoters may be used to bond the photoresist to thesemiconductor substrate or other device surface until the photoresist isexposed to light, thereby defining feature edges and boundaries withinthe device. Photoresist, however, may persist around the substratesurface and photoresist interface. This is because some regions towardthe bottom of the photoresist may not become sufficiently soluble afterbeing exposed to an incident radiation to be completely removed, andinstead remain bonded to the substrate by the adhesion promoter. Theseareas of persisting photoresist may correspond to areas where anincident radiation signal is weakest due to radiation absorption byphotoresist or reflective interaction effects between the substrate andphotoresist.

A prior art technique for addressing the shortcomings of traditionaladhesion promoters is the use of a photoactive adhesion promoter.Photoactive adhesion promoters contain photoacid generators (PAGs),which react to incident light by releasing acid in regions in which thephotoresist is exposed to the light. The acid helps to remove thephotoresist from these regions, thereby improving the accuracy offeatures defined by the presence of photoresist.

FIG. 1 illustrates a prior art photoadhesion promoter moiety comprisinga PAG. The prior art example of FIG. 1 illustrates a system that iscapable of attaching a PAG material to a semiconductor wafer as aself-assembled layer. The photoactive adhesion promoter of FIG. 1comprises an adhesion promoter and a PAG. The PAG comprises a photonharvesting group and a catalyst group. In the embodiment illustrated inFIG. 1, the adhesion promoter is trimethoxysilane, the photon harvestinggroup is methyldiphenylsulfonium, and the catalyst group isnonafluorobutanesulfonate. In addition, a linker bonds the adhesionpromoter to the photon harvesting group.

The adhesion promoter, photon harvesting group, and the catalyst groupmay comprise different compounds as well. For example, the adhesionpromoter may comprise alkoxysilane, silylchloride (a subclass ofsilylhalide), phosphate, phosphonate, alkene, thiol, or sulfide,

The photon harvesting group may comprise sulfonium salts, such astriarylsulphonium. Triarylsulphonium is a general class, in which arylrepresents any structure with an aromatic group bound to the sulfur atomas well as functionalized aryl groups where functionalization may beheteroatoms, such as fluorine, chlorine, bromine, and functional groupssuch as alcohol (OH), nitro (NO₂), amine (R₃N), amide (R₂NC(O)R),carboxylic acid (RCOOH), ester(RCOOR), ether (ROR), carbonate(ROC(O)OR).

Furthermore, alkyldiarylsulfonium and dialkylarylsulfonium are a generalclass of sulfonium salts which may be used, in which aryl is defined asabove and alkyl is a hydrocarbon group, such as (CH₂)_(n)CH₃ where n=0to 11, as well as functionalized hydrocarbon groups, in whichfunctionalization may be heteroatoms, such as fluorine, oxygen,nitrogen, chlorine, bromine and functional groups such as alcohol (OH),nitro (NO₂), amine (R₃N), amide (R₂NC(O)R), carboxylic acid (RCOOH),ester(RCOOR), ether (ROR), or carbonate (ROC(O)OR). Alternatively, thephoton harvesting group may comprise iodonium salts, such as diaryl andalkyaryl, in which aryl and alkyl are as defined above.

The catalyst group may comprise alternative compounds, such asperfluoroalkylsufonate, alkylsutfonate, arylsulfonate, perfluoroalkyl,alkyl and aryl phosphate, or fluoroalkylsulfonamide.

Other photoadhesion promoters include sulfides, nitroaryl derivatives,or aryl sulfates (for example, tosylates). PAGs may include sulfide andonium type compounds such as diphenyl iodide hexafluorophosphate,diphenyl iodide hexafluoroarsenate, diphenyl iodidehexafluoroantimonate, diphenyl p-methoxyphenyl triflate, diphenylp-tert-butylphenyl triflate, diphenyl p-isobutylphenyl triflate,diphenyl p-tert-butylphenyl triflate, triphenylsulfoniumhexafluorophosphate, triphenylsulfonurn hexafluoroarsenate,triphenylsulfonium hexafluoroantimonate, bis-(t-butylphenyl)iodoniumtriflate, triphenylsulfonium triflate, triphenylsulfoniumnonafluorobutylsulfonate, diphenyliodoniumheptadecafluorooctylsulphonate, and dibutyinaphthysulfonium triflate, aswell as the combinations and permutations of the above moieties.

Examples of photo-base generators (PBGS) may include nitrocarbamate orquaternary ammonium dithiocarbamate and other generators described in,for example, Prog. Polym. Sci., volume 21, 1-45 (1996 Elsevier Science,Ltd.) or in J. Polym. Sci. Part A: Polym. Chem., 39, 1329-1341 (2001).

Sacrificial light absorbing material (SLAM) is typically used to fillholes or trenches in the surface of various semiconductor material (e.g.substrate material) before subsequent processing layers are added.Furthermore, SLAM materials are useful in that they absorb incidentlight, thereby reducing the effect of sporadic photoresist destructionthat can result from light reflected from the material exposed to thelight. SLAM is typically spun on to a wafer material and later etched,leaving SLAM in the holes or trenches within the surface in order tocreate a relatively smooth surface.

FIG. 2 illustrates a prior art dual damascene process, in which aphotoresist layer (including a PAG) and a SLAM layer are deposited on asemiconductor surface. A mask layer can be applied, exposing thephotoresist layer to incident radiation (ultra-violet light, extremeultra-violet light, electron beam, x-ray, etc.) in areas that are notcovered by the mask layer, removing photoresist from the exposed areas.

Prior art processing techniques typically require at least twoprocessing steps to apply a PAG (typically contained within thephotoadhesion promoter of the photoresist) and a SLAM to the wafer. Thisis because the PAG is typically included in the photoresist, which isapplied after the SLAM. Using extra process step or steps to apply PAGand SLAM to a wafer can be costly in terms of processing time and waferyield, as these steps require time and serve as a potential source ofdefects within the process.

Furthermore, prior art semiconductor processing techniques, such asthose used in a damascene process flow, typically require a bake step,in which the wafer can be heated to extreme temperatures. During a bake,the wafer and SLAM may become porous, allowing amines to be releasedfrom the silicon material in the wafer, which can get trapped within asuperjacent ILD layer and/or migrate ‘upward’ to the photoresist layer.

FIG. 2 illustrates the migration path of amines released from the waferthat get trapped in the ILD and then migrate up to the photoresistlayer. The amines trapped in the ILD can flow through the SLAM and reactwith an overlying photoresist layer, thereby deteriorating (“poisoning”)the photoactive properties of the photoresist. Resist poisoning canresult in a photoresist residue that cannot react with incident light,and therefore remains after the photoresist is developed, causingfeatures within the semiconductor device to be deformed.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments and the invention are illustrated by way of example and notlimitation in the figures of the accompanying drawings, in which likereferences indicate similar elements and in which:

FIG. 1 illustrates a prior art photoactive adhesion generator (PAG)compound.

FIG. 2 illustrates a prior art damascene process in which a sacrificiallight absorbing material (SLAM) is applied in a separate process stepfrom the application of a PAG.

FIG. 3 illustrates a compound containing a PAG material and a SLAMmaterial according to one embodiment of the invention.

FIG. 4 illustrates a process for forming a photoactive adhesion promoterand a photoresist layer on a semiconductor substrate according to oneembodiment of the invention.

FIG. 5 illustrates one embodiment of the invention, in which a PBL isdeposited between the SLAM layer and the photoresist layer.

FIG. 6 illustrates a SLAM having a sulfonium PAG covalently attachedthereto, according to one embodiment of the invention.

FIG. 7, on the other hand, illustrates a non-ionic PAG having a basequenching compound attached thereto.

FIG. 8 further illustrates a SLAM having sulfonium hydroxide covalentlyattached thereto.

DETAILED DESCRIPTION

Embodiments of the invention described herein help reduce semiconductorprocess effects, such as undesired line edge roughness, insufficientlithographical resolution, and limited depth of focus problemsassociated with the removal of a photoresist layer. More particularly,embodiments of the invention use a photoacid generator (PAG) material inconjunction with a sacrificial light absorbing material (SLAM) to helpreduce these and other undesired effects associated with the removal ofphotoresist in a semiconductor manufacturing process. Furthermore,embodiments of the invention allow a PAG to be applied in asemiconductor manufacturing process in an efficient manner, requiringfewer processing operations than typical prior art techniques.

In at least one embodiment of the invention, a SLAM material containinga PAG material is applied to a semiconductor surface. Excess SLAM/PAGmaterial may then by removed from the surface, leaving SLAM/PAG withinany holes or trenches created during the course of semiconductorprocessing within a semiconductor surface. The SLAM/PAG material thatremains within the holes of the semiconductor surface helps to create asubstantially smoother surface than without the use of the SLAM/PAG. TheSLAM/PAG remaining in the holes and irregularities of the surfaceadditionally contribute to a more anti-reflective surface, such thatincident radiation used to develop the photoresist does not sporadicallyreflect from the surface to the surrounding photoresist.

The SLAM itself can absorb light, thereby helping to reduce the amountof incident light that is reflected from the surface to which thephotoresist is being applied. PAG material releases an acid when exposedto incident light, thereby assisting in the removal of photoresist fromthe exposed regions. Including the PAG material within the SLAM, in oneembodiment, helps to create more accurate features within the exposedregions vis-à-vis the acid released by the PAG material when exposed toincident light. Furthermore, because some embodiments of the inventioncombine SLAM and PAG material, only the process operations necessary toapply the SLAM material are necessary to apply the PAG material, therebyimproving the efficiency of the process over the prior art.

FIG. 3 illustrates a PAG 301, such as the one illustrated in FIG. 1,covalently bonded to a SLAM material 305, according to one embodiment ofthe invention. In one embodiment, the PAG is bound to the SLAM through areaction of the trialkoxysilane with pendant groups (e.g. Si—OH groups)within the SLAM material, forming silylether linkages. In one embodimentthe PAG is bound to the SLAM via covalent bonds that attach a lightharvesting group and a catalyst (in this case a PAG) to the SLAMmaterial. In other embodiments, an admixture of PAG and SLAM materialwould bind the PAG to the SLAM. In addition to the PAG materialpreviously discussed, the PAG may include a monomer, such as(3-diphenylsulfoniumpropyl) trimethoxysilane trifluoromethanesulfonate(see FIG. 9 a), (3-diphenylsulfoniumpropyl) trimethoxysilanenonafluorobutanesulfonate (see FIG. 9 b), 3-diphenylsulfoniumpropyl)trimethoxysilane iodide (see FIG. 9 c).

Other embodiments may involve other reactions, depending upon variouspatterning and resist requirements. For example, in one embodiment, aphotobase is used instead of or in addition to the PAG, which would havean opposite effect upon the photoresist-wafer interface than using a PAGalone. Furthermore, in other embodiments, a combination of photobase andphotoacid sensitivity would allow further control of the photoresistprofile, including reduction of footing and line edge roughness, such asin the bottom of trench patterns and contact patterns, as well assubstrate compatibility. In other embodiments, the PAG and/or photobasemay be blended with other compounds to provide further control ofphotoresist removal.

FIG. 4 illustrates a process in which a SLAM/PAG material is formed in asemiconductor device according to one embodiment of the invention. Atoperation 401, an etch stop layer is deposited, and at operation 405, anILD is deposited superjacent to the etch stop layer. At operation 410, atrench is made in the ILD and etch stop and SLAM (including PAG) isdeposited in the trench at operation 415. In other embodiments, theremay be more operations involved to perform other processing steps, suchas deposition of photoresist, development of photoresist, etc. However,embodiments of the invention deposit a PAG in the same processingoperation as the SLAM deposition.

In addition to amines released from the wafer and inter-layer dielectric(ILD) as a result of a bake process, amines may also be generated insome embodiments of the invention by introducing a PAG within a SLAM.Accordingly, some embodiments of the invention reduce photoresistpoisoning that can result from amines reacting with the photoresistlayer by including a poison buffer layer (PBL). In one embodiment, a PBLis deposited between the SLAM layer (including a PAG) and a photoresistlayer in order to substantially prevent amines released during ahigh-temperature bake operation, or otherwise, from coming into contactwith the photoresist layer.

FIG. 5 illustrates one embodiment of the invention, in which a PBL isdeposited between the SLAM layer and the photoresist layer. Thesemiconductor device illustrated in FIG. 5 includes an etch stop layer515, an ILD layer 510, a SLAM layer 501, and a photoresist layer 505. Bydepositing a PBL 520 between the SLAM layer and the photoresist layer,the embodiment illustrated in FIG. 5 can help prevent amines traversing508 from the ILD through the SLAM layer from coming into contact withthe photoresist layer.

In at least one embodiment of the invention the PBL contains anycarbon-based polymer that reacts sufficiently with amines to prevent theamines from poisoning the photoresist, including polymer blendedcompounds, such as poly-t-butyl vinylcarbamate, plyacetaldehyde withpolyvinylchloride, and polyorthonovolaks with trichlorotriazine. Inother embodiments, other polymers or polymer blended compounds may beused that react with amines. Furthermore, in other embodiments, the PBLlayer may be deposited between other materials illustrated in FIG. 5. Inother embodiments, the PBL may be integrated with at least one materialillustrated in FIG. 5.

The semiconductor features illustrated in FIG. 5 may be formed as partof a damascene process, in one embodiment of the invention. In otherembodiments of the invention, the features of FIG. 5 are formed as partof a dual damascene process. However, embodiments of the inventionillustrated in FIGS. 3-5 may be applied to any semiconductor process inwhich photoresist is applied to a surface which includes an ILD orsimilar structure.

Diffusion of amines into the photoresist may be further ameliorated bybinding the amines to the polymer backbone of the PAG in one embodiment.In one embodiment of the invention, amines can be bound to the polymerbackbone by introducing a basic property to the photoresist and linkingthe base to the polymer backbone. Alternatively or additionally, someembodiments reduce the diffusion of amines into the photoresist byintroducing photoactive base compounds, such as photo-decomposable bases(PDBs) and photo-generated bases (PGBs), to the SLAM/photoresistinterface.

Introducing PDBs, such as sulfonium hydroxides, to the SLAM/photoresistinterface can increase the pH contrast between exposed and unexposedregions of the interface, in one embodiment, whereas introducing PGBs,such as quaternary ammonium dithiocarbamate and/or alpha-keto carbamate,would decrease the pH contrast between the exposed and unexposedregions. By way of example, FIG. 6 illustrates a SLAM 605 having asulfonium PAG 610 covalently attached thereto, according to oneembodiment of the invention. FIG. 7, on the other hand, illustrates aSLAM 705 coupled to a non-ionic PAG 710 and a base quenching compound715 attached thereto. FIG. 8 further illustrates a SLAM 805 having a PAG810 and a sulfonium hydroxide PDB 815 covalently attached thereto.Moreover, other ionic and non-ionic PAGs could be used in the examplesillustrated in FIGS. 6-8 in other embodiments of the invention.

Various materials may be used in the embodiments of the invention. Forexample, the substrate surface may be doped silicon, silicon dioxide,carbon doped silicon dioxide (CDO) or other substrate materials. Thecompounds illustrated in FIGS. 6-8 may be used in a damascene process,in one embodiment of the invention. In other embodiments of theinvention, the compounds of FIGS. 6-8 are used as part of a dualdamascene process. However, embodiments of the invention illustrated inFIG. 6-8 may be applied to any semiconductor process that includes SLAMand photoresist deposition.

While the invention has been described with reference to illustrativeembodiments, this description is not intended to be construed in alimiting sense. Various modifications of the illustrative embodiments,as well as other embodiments, which are apparent to persons skilled inthe art to which the invention pertains are deemed to lie within thespirit and scope of the invention.

1. A semiconductor process comprising: forming an etch stop layer;forming an ILD superjacent to the etch stop layer; etching a trenchwithin the etch stop layer and the ILD; depositing a sacrificial lightabsorbing material (SLAM) within the trench, the SLAM comprising aphotoactive generator (PAG).
 2. The process of claim 1 furthercomprising forming a poison barrier layer (PBL) superjacent to the SLAM.3. The process of claim 2 further comprising applying a photoresistlayer superjacent to the PBL.
 4. The process of claim 3 furthercomprising exposing a portion of the photoresist to incident light. 5.The process of claim 4 further comprising a bake operation, during whichamines are generated.
 6. The process of claim 5 wherein the PBLcomprises a compound blend chosen from a group consisting of:poly-t-butyl vinylcarbamate, plyacetaldehyde with polyvinylchloride, andpolyorthonovolaks with trichlorotriazine.
 7. The process of claim 6wherein SLAM comprises either a photo decomposable base (PDB) or a photogenerated base (PGB) to neutralize amines generated by bonding the PAGwith the SLAM.
 8. The process of claim 7 wherein the PBL helps toprevent amines generated during the bake operation from reacting withthe photoresist layer.
 9. The process of claim 8 comprising a dualdamascene process.
 10. The process of claim 9 wherein the PAG bonds tothe photoresist via a chemical catalyst group comprisingnonafluorobutanesulfonate.
 11. The process of claim 10 wherein the PAGis coupled to a photon harvesting group to enhance solubility of thephotoresist, the photon harvesting group comprisingmethyldiphenylsulfonium.
 12. A semiconductor device comprising: aphotoresist layer; a poison buffer layer (PBL) subjacent to thephotoresist layer to prevent amines from reacting with the photoresistlayer; sacrificial light-absorbing material (SLAM) subjacent to the PBL,the SLAM including a photoactive generator (PAG) material.
 13. Thesemiconductor device of claim 12 wherein the SLAM comprises photoactivebase compounds to neutralize amines generated in the SLAM.
 14. Thesemiconductor device of claim 13 wherein the photoactive base compoundscomprise sulfonium hydroxides.
 15. The semiconductor device of claim 13wherein the photoactive base compounds comprise quaternary ammoniumdithiocarbamate and/or alpha-keto carbamate.
 16. The semiconductordevice of claim 13 wherein the PBL comprises a compound blend chosenfrom a group consisting of: poly-t-butyl vinylcarbamate, plyacetaldehydewith polyvinylchloride, and polyorthonovolaks with trichlorotriazine.17. The semiconductor device of claim 16 further comprising an ILDsubjacent to the SLAM layer.
 18. The semiconductor device of claim 17further comprising an etch stop layer superjacent to the ILD layer. 19.The semiconductor device of claim 18 comprising a trench etched into theetch stop and the ILD, the trench being filled by the SLAM.
 20. Thesemiconductor device of claim 19 wherein the semiconductor device iscreated, at least in part, using a damascene semiconductor process. 21.The semiconductor device of claim 20 wherein the PAG includes a monomerchosen from a list consisting of: (3-diphenylsulfoniumpropyl)trimethoxysilane trifluoromethanesulfonate, (3-diphenylsulfoniumpropyl)trimethoxysilane nonafluorobutanesulfonate, 3-diphenylsulfoniumpropyl)trimethoxysilane iodide.